So I currently have a Pioneer BDR-206DBK that I have been using to rip my BD and DVD collection, but find that I have so many discs it is taking forever. I hooked up a DVD drive as well, and it seems that there is no problem ripping a BD and a DVD at the same time to a USB 3.0 external drive (Toshiba Canvio 1TB) using MakeMKV, so I ordered another BD drive (UH12NS29) so I can do 2 BD discs at the same time as the majority of my collection is BD.

A friend of mine has a spare BD drive that he told me I could have for cheap as he doesn't use it much. Do you think I would be able to do 3 rips to one drive at once or would that be too much?

I also just bought 4x4TB Seagate ST4000DM000 that I have yet to install, but plan to use in either Raid 5 or 10 for storage and will be streaming all my rips to a couple of HTPC. I just like to do the rips to the separate HDD, do all the compression in Handbrake, remux the subs, etc before moving them to their final location.

I sometimes rip three blu-rays at once on my ripping computer. At the fastest point of the disc, it can approach 30MB/s ripping speed, so three at once would peak at 90MB/s ripping speed, but since the fastest part of the disc is rarely synchronized between the three, the actual top speed is almost always less than that. I'd say you can safely figure that the required throughput would almost always be less than about 60 to 70MB/s.

The limiting factor is the 4K random write performance of your HDD, which probably tops out ~60MBps.

No, and not even close.

The limiting factor is definitely NOT the 4K random write performance of your HDD, since the writes will be mostly sequential and significantly larger chunks than 4KiB (probably around 128KiB).

And although not relevant here, no HDD has a 4K random write performance anywhere near 60MBps (only an SSD can hit those speeds). HDDs are lucky to exceed 1MB/s for 4K random write.

Also, I did NOT recommend staggering the start of ripping for each disc. That is not necessary, since each disc is different and it is unlikely that they will each hit the peak throughput at the same time. And besides, even if they did peak at the same time, a good HDD can probably still keep up.

A single layer Blu Ray will peak ~45-54MBps in a 12x drive, with a dual layer Blu Ray peaking ~35MBps. Every movie I've ripped followed the same pattern. It started out slow (1-3x), ramped up to its peak (8-12x) and tapered off at the end. Most movies are the same length (~1h30m), so it stands to reason that many will peak around the same time.

No, I did not say (and do not say) that the peak sequential write speed of an HDD will be reached (in aggregate) when you are writing three streams to an HDD. However, the aggregate speed is often only a little worse if the three streams are each sequential and using chunk sizes of 128KiB or larger. To put a number on it, if you have an HDD capable of a peak sequential speed of 100MB/s, I would expect it to be capable of at least 60-70MB/s when writing 3 large sequential streams.

As for your blu-ray throughput estimate, you are quoting unrealistic numbers in my experience. Yes, the maximum allowed (by blu-ray spec) 1X throughput of a blu-ray is 6.75MB/s (54Mbps), and a single-layer 12X reader could theoretically hit 12 times that, which is 81MB/s. But in reality, I've never seen a single blu-ray exceed 50MB/s peak speed, and yes, I do have a drive capable of 12X single-layer ripping. Besides, single-layer discs are rare, and the peak speed is at the end, not the middle like dual-layer discs.

For dual-layer discs, the fastest drives can rip at 8X, but again, I have never seen the theoretical maximum of 54MB/s (=8x6.75). Typical peaks are in the low 30MB/s range, and I have never seen over 40MB/s for one dual-layer blu-ray. And, of course, those are peak speeds, which are only achieved for a couple minutes in the middle of a dual-layer blu-ray rip. All the dual-layer discs that I have seen have the data at the outer edges of the disc (the unused space is always the inner tracks of the disc), equally divided between each layer, and the stream starts at the inner portion, so as you say, the speed gradually goes up, hits a peak at the outer edge of the disc on the first layer, then switches to the second layer and gradually slows down as it reads towards the inner portion of the disc on the second layer.

But since blu-rays movies have a variety of lengths (not just the movie length, but also the extra material included on the disc will have an effect on when the speed peaks) and a variety of bit-rates, both the peak speed and the time after ripping is started when the peak speed is reached will vary from disc to disc. And it does. In my experience of ripping 3 discs at once (and just starting them as quickly as I can type in the information for each one, so probably less than 1 minute of staggering the start times), there is no problem ripping to a single HDD and the aggregate peak throughput almost never exceeds 60-70MB/s.

I am ripping two Blu Ray discs right now, and at the same time transferring a bunch of files from the disc being written to to another disc and everything seems to be working great. Makes me think ripping three at the same time would probably be ok too.

A little update, as I am finally happy with my setup. I have found it no trouble to rip 3 discs at once, but have actually gone to a 4 drive setup ripping to two 1 TB drives.

I am very interested to hear if you have had any issues ripping multiple disks at once? Even more interested because you computer is close to what I am currently specking out to build from newegg. I was thinking of getting a case with 4 optical bays and 4 or more hard drive bays and rip a disk to each drive set up a long que and do the transcoding over night. I would love to learn more about how you are set up and what is working for you and what would work different next time.